Skip to main content

Full text of "The manufacture and properties of iron and steel"

See other formats


SEGREGATION AND HOMOGENEITY.
237
steel, particularly if it is heated for a long time, as in the case of large ingots, and also if it undergoes two different heatings and coolings, as in the case of ingots rolled into slabs or blooms, and then reheated to be rolled into plates or angles. During each heating and rolling and cooling there must be a redistribution and equalization of carbon in obedience to the laws of cementation, and since the largest ingots are kept longest in the heating furnaces, it follows that this one condition of larger mass, which is favorable to segregation, is partially self-corrective.
The best-known paper on the irregularity of steel is by Pourcel,* "but, unfortunately, it reads like an ex parte argument to prove that because some steels exhibit serious irregularities, therefore all steels have the same fault. I shall try to show that all steels do not exhibit excessive concentration of impurities, that the highly segregated portions of an ingot are often small isolated areas in the interior of the mass, and that by using a steel of low phosphorus it may be assumed that the finished material is practically uniform. . SEC. Xlllb.—Segregation in steel castings.—The most extreme instances of irregularity would be expected in large masses cast in sand, and cooled slowly. Pourcel states that in the pipe cavity of such a casting a cake of metal was discovered which was separate from the surrounding walls. The composition of this formation, together with that of the walls of the pipe cavity and of the mother metal, is given in Table XIII-A. It should be noted that the original metal contained a higher proportion of phosphorus than should be present in steel castings, so that the conditions were favorable to segregation.
TABLE XIII-A.
Extreme Segregation in Pipe Cavity.
Origin of test.		Composition; per cent				Mn.
		C.	Si.	S.	P.	
Ladle test Wall of pi Cake, two		.240 .680 1.274	.336 .326 .410	.074 .825 .418	.089 .318 .753	.970 1.490 1.080
						
	nches thick in pipe cavity ....					
As testimony in an opposite direction, I found no segregation in a steel roll made by The Pennsylvania Steel Company.  This was
* Segregation and its Consequences in Ingots of Steel and Iron.   Trans. A. I, M. .E., Vol. XXII. p. 105.                          ,                                                            ..............